Greek National Road 16a is a national highway in Chalkidiki, Central Macedonia, Greece. It connects Polygyros with Greek National Road 16 near Agios Prodromos.
It functions as a short, but important branch, allowing direct access of Polygyros to the main road network to Thessaloniki and the rest of Chalkidiki. It is approximately 15 kilometers long.
Ministerial Decision G25871 of 9 July 1963 created the EO16a from the Polygyros branch of the old EO40, which existed by royal decree from 1955 until 1963.